1. Technical Field
The present invention relates to a technique to display images using electro-optical material such as liquid crystal.
2. Related Art
In electro-optical devices such as liquid crystal devices, a plurality of pixels aligned so as to correspond to the intersections of a plurality of scanning lines and a plurality of data lines is driven by driving circuits, such as scanning line driving circuits and data line driving circuits. A technique applicable to the electro-optical devices is disclosed in Japanese Unexamined Patent Application Publication No. 2003-263134 (see Paragraph 0043 and FIG. 2). In this technique, a driving circuit is controlled in accordance with various parameters written in a register. The parameters stored in the register are changed as necessary in accordance with a command input from an external device, such as a CPU in an electronic device in which the liquid crystal device is incorporated. With this type of electro-optical device, display may be interrupted due to a sporadic incident, e.g., when a battery is removed from the electronic device. In this case, a command to halt display is input from the external device and thus display is halted after the parameters have been initialized in accordance with the command.
In a liquid crystal device using liquid crystal as the electro-optical material, electric charge may remain in pixels, namely, liquid crystal capacitors, after halting display. If remaining electric charge keeps applying direct voltage to the liquid crystal, the orientation of the liquid crystals is changed to be different from the predetermined orientation, resulting in degradation in display quality. To address this problem, in a technique disclosed in Japanese Unexamined Patent Application Publication No. Hei 9-269476 (see Paragraph 0018 and FIG. 3), turn-off voltage is applied to all pixels after halting display (referred to as power-off-sequence process hereinbelow). With this technique, since electric charge stored in the pixels is discharged before halting display, degradation in liquid crystal characteristics due to application of direct voltage is suppressed.
Preferably, in the liquid crystal display disclosed in Japanese Unexamined Patent Application Publication No. 2003-263134, when a command to halt display is issued, a power-off-sequence process is performed and then the parameters are initialized, thereby halting display. With this liquid crystal display having the aforementioned construction, however, after completion of the power-off-sequence process, the parameters are initialized. Therefore, if a command to change the parameters is input from the external device during the power-off-sequence process to change the parameters, the parameters are initialized after the power-off-sequence process and thus the command is not reflected on the liquid crystal display. Specifically, a command to halt display is often input when an emergency occurs and other commands tend to be input one after another to solve the emergency. This may lead to a serious problem in the liquid crystal device having the aforementioned construction since the commands cannot be accepted during the entire power-off-sequence process. The present invention is designed to solve the aforementioned problems and it is an object of the present invention to provide a mechanism to accept a command input from an external device in an electro-optical device in which a power-off sequence process is performed in advance of halting display.